Modern agricultural practices rely heavily on precise and timely applications of fertilizers, herbicides, pesticides and other chemicals. In situations where the applications must be made to standing row crops, such as corn or beans, liquid or granular materials are often applied using a high ground clearance, self-propelled applicator.
In order to provide maximum ground clearance, such applicators utilize highly specialized suspension and propulsion systems for connecting the ground engaging wheels of the applicator to a frame of the applicator. Typically, separate hydraulic drive propulsion motors are provided as part of the suspension, for each drive wheel, to thereby further enhance ground clearance by minimizing the encroachment of typical drive train or suspension components into the space between the wheels under the applicator.
Sometimes it is necessary to operate these applicators under conditions of very high ambient temperatures, approaching the operational limit ratings of the applicator, in order to get the necessary chemicals applied within a narrow window of time when the chemicals will provide maximum benefit to the crops.
To improve operational effectiveness and efficiency, self-propelled agricultural product applicators have gotten larger and heavier, so that they can carry larger payloads of agricultural product, and cut down the time lost to refill the applicator. Modern applicators are typically also designed to operate at high speeds, up to 40 miles per hour, for example, while applying the agricultural product.
The combined effect of high ambient temperature, payloads and operating speeds can cause significant heating of the hydraulic fluid in the drive systems of modern self-propelled product applicators. Dealing with such heating of the hydraulic fluid in applicators that may operate need to operate continually for many hours under high ambient temperature conditions presents considerable challenges for designers of such applicators. Virtually all components of the hydrostatic drive system, and associated fluid coolers, fans, etc., must be considerably oversized, beyond requirements for normal temperature operation, in order maintain full rated operation of the applicator during occasional periods of unusually high ambient temperatures.
Such oversizing of the applicator and its components, solely to provide operation in rarely occurring ambient conditions is not desirable for a number of reasons. As the applicator itself becomes bigger and heavier, the payload of agricultural product that can be carried must typically be undesirably reduced. Bigger and heavier components required to deal with increased fluid heating at high ambient temperature also undesirably drives up manufacturing and operating costs, and the initial price of the applicator.
It is desirable, therefore, to provide an improved form of a self-propelled agricultural applicator, and improved systems and methods for operating such an applicator that allow for occasional operation at high ambient temperature conditions, without resorting to oversizing of many of the components that may be affected occasional operation of the applicator near the upper limits of rated operating temperatures.